Process for the production of cyclic esters



United States Patent 3,278,558 PROCESS FOR THE PRODUCTION OF CYCLICESTERS Paul N. Rylauder, Newark, N.J., and Lewis M. Berkowitz,

Baltimore, Md., assignors to Engelhard Industries, Inc.,

Newark, N.J., a corporation of Delaware No Drawing. Filed June 11, 1965,Ser. No. 463,332

Claims. (Cl. 260343.5)

This is a continuation-in-part application of our copending applicationSerial No. 150,867, filed November 8, 1961, now abandoned, which in turnwas a continuation-in-part of our copending application Serial No.713,559, filed February 6, 1958, now abandoned.

This invention relates to the production of cyclic esters and moreespecially to a new and improved oxidation process for preparinglactones wherein ruthenium tetroxide is the oxidant, and characterizedby being carried out in a non-violent and controllable manner.

Use of ruthenium tetroxide for oxidizing various organic compounds, [forinstance aldehydes, acetylenes, amides, and hydroxy compounds, is knownin the prior art. However, such oxidation with ruthenium tetroxide hasheretofore been unsatisfactory for the reason the oxidation hasgenerally been a violent, explosive, non-controllable reaction, withcomplete or virtually complete degradation or destruction of the organiccompound being oxidized whereby the desired oxidation products were notobtained.

In accordance with the present invention, a process is provided foroxidizing cyclic ethers employing ruthenium tetroxide as oxidant in anon-violent, readily controlled manner to obtain cyclic esters orlactones. The process involves oxidizing the cyclic ether of the formulawherein Alk is an unsubstituted or substituted methylene radical and nis an integer of 2-20 inclusive in solution in an inert or substantiallyinert liquid solvent at a temperature maintained in the range of 0 C. to20 C. inclusive. The lactone obtained as product of such process has theformula (Alk)n wherein Alk and n have the meaning previously disclosedherein.

Exemplary of the inert or substantially inert liquid solvents for use inthe process are carbon tetrachloride, chloroform, paraflinichydrocarbons, erg. hexane, heptane, Z-methyloctane and 3-methyloctane,uaphthenes, e.-g. cyclopentane, cyclohexane, methylcyclopentane andmethylcyclohexane, acetone, ethyl acetate, buty-ro'lactone and water.

Exemplary of ethers oxidized in accordance with the invention aretetrahydroifuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran,2,3-diethyltetrahydrofuran, 2,3- dimethyltetrahydrofuran,3-hexyltetrahydrofuran, tetrahydropyran, 2 methyltetrahydropyran,"3-ethyltet-rahydropyran, 4 butyltetrahydropyran, 2,3-d-iethyltetrahydropyran, and 2,3,4-trimethyltetrahydropyran. Product lactones obtained bythe oxidation of these cyclic ethers are, respectively, abutyrolactone;-methyl-y-butyrolactone; a mixture of a-methyl- -butyrolactone andB-methyl-' butyrolactone; [Ly-diethyl-v butyrolactone; [3,y-dimethyl-'y-butyrolactone; a mixture of a-hexylbutyrolactone andfl-hexyl-y-butyrolactone; A-valerolactone; A-methyl-A- valerolactone; amixture of a-ethyl-A-valerolactone and 'yethyl-A-valerolactone;B-butyl-A-valerolactone; 'y,A-diethyl-A-vale-rolactone; ,B,-,,A-trimethyl-A-valerolactone.

ice

The cyclic ethers herein react with the R110 as follows:

:ivigh Alk and it having the significance previously speci- The reactiontemperature of 0 to 20 C. are essential to the success of the presentinvention for the reason that at temperatures much above 20 C. theviolent and uncontrollable reactions occur even in the presence of theinert solvent. At temperatures much below 0 C. the reaction takes placetoo slowly to be commercially practicable, typically requiring reactiontimes of 1 week or longer. Temperatures of 0 to 10 C. are preferred forthe rea son that by observing the 10 C. upper limit, excessive oxidationis minimized. Preferred solvents rfor forming this solution of the etherprior to the oxidizing are carbon tetrachloride, chloroform, theparafiinic hydrocarbons and naphthenes, inasmuch as the rutheniumtetroxide tends to undergo a slow reaction with the remaining solventswhich are oxygenated compounds.

Tetrahydroifuran was smoothly oxidized herein to gamma-butyrolactone innearly quantitative yield. Whatever activating efiect the oxygen of theether linkage exerts on the adjacent methylene group is absent in theester. The gannna butyrolactone was stable toward further oxidation andattempts to carry the oxidation thereof to suecinic anhydride wereunsuccessful.

The ruthenium tetroxide may be present in an amount stoichiometricallyequivalent to the cyclic ether to be oxidized or in slight excess overthis amount.

The pressure is preferably atmospheric, as superatmospheric orsubatmospheric pressures afford no particular advantages although thesepressures may be employed. The reaction time may be in the range of afew seconds to one hour, usually a few seconds to a few minutes.

The invention will be .fiurther illustrated by reference to thefollowing specific examples:

EXAMPLE I Preparation of ruthenium tetroxide A solution of 4.37 grams ofruthenium trichloride, containi-ng 18 percent water, in ml. of 0.5 Nhydrochloric acid was placed in a 200 m1. round bottom flask and heatedto boiling temperature. A 1 N sodium bromate solution was addedgradually to the reaction mixture through a thistle tube, provided witha stopcock. The tube passed down through a short air condenser which wasconnected at the top by a side arm to an ice cooled trap. Glassconnections were used throughout. Ruthenium tetroxide volatilized as itwas formed and was collected in the cooled trap. Sodium bromate wasadded in portions until rEu-rther addition failed to generate moreruthenium tetroxide. The supernatant water was removed by a capillarydropper and the residue of ruthenium tetroxide, weighing 1.5 grams, wasdissolved in 10 ml. of carbon tetrachloride, to produce a deep redsolution. The yield of ruthenium tetroxide in a number of suchpreparations averaged 55 percent.

EXAMPLE II A ruthenium tetroxide solution, prepared according to theprocedure of Example I and containing 1.51 grams of ruthenium tetroxideon a solvent-free basis, was added dropwise with stirring to a solutionof 1.5 grams of tetrahydrofuran in 10 ml. of carbon tetrachloride,cooled in an ice bath to maintain a temperature of 10 to 15 C. Theoxidation proceeded in a non-violent and easily controllable manner toproduce 'y-buty-rolactone, identified by Patented Oct. 11, 1966-infrared spectrogram. The melting point of the derivative,phenylhydrazide, obtained therefrom was 8889 C.

EXAMPLE III A solution is made up of tetrahydropyran in carbontetrachloride. To this solution is added dropwise a solution ofruthenium tetroxide prepared according to the procedure of Example I andcontaining 1.51 grams of ruthenium tetroxide (solvent-free basis). Thesolution of tetrahydropyran is maintained at a temperature of 15 C. to20 C. by cooling in an ice bath during the addition of the rutheniumtetroxide solution. The oxidation reaction proceeds in a non violent andnon-explosive manner and is easily controlled to producea-valerolactone.

What is claimed is 1. A process for the preparation of a lactone of theformula wherein Alk is from the group consisting of unsubstituted andsubstituted methylene radicals and n is in integer of 3 to 4 inclusive,which comprises oxidizing a cyclic ether of the formula (Anon whereinAlk and n are as aforesaid with ruthenium tetroxide in solution in asubstantially inert liquid solvent at a temperature maintained in therange of C. to 20 C. inclusive there-by effecting the oxidation in anon- 5 violent and controllable manner.

2. A process in accordance with claim 1 wherein the solvent is carbontetrachloride.

3. A process in accordance with claim 1 wherein the solvent is water.

4. A process in accordance with claim 1 wherein the cyclic ether istetrahydrofuran and the product lactone is w-butyrolactone.

5. A process in accordance with claim 1 wherein the cyclic ether istetrahydropyran and the product lactone is fi-valerolactone.

References Cited by the Examiner UNITED STATES PATENTS 2,020,298 11/1935Carother et al 260343 2,453,890 11/1948 Bremmer et al. 260343.5

FOREIGN PATENTS 610,166 10/1948 Great Britain. 900,107 7/1962 GreatBritain.

WALTER A. MODANCE, Primary Examiner.

JAMES A. PATTEN, Assistant Examiner.

1. A PROCESS FOR THE PREPARATION OF A LACTONE OF THE FORMULA 